The present invention relates to an ultraviolet/infrared absorbent low transmittance glass. More particularly, it relates to an ultraviolet/infrared absorbent low transmittance glass having a grayish green shade, a low visible light transmittance, a low solar energy transmittance, and a low ultraviolet transmittance, so that it is useful for windows of vehicles or buildings particularly for a privacy protecting glass in a rear window of a vehicle.
Recently, a variety of glasses with capable of absorbing ultraviolet/infrared light to be used as a vehicle windshield has been proposed for preventing degradation of luxurious interior materials and reducing cooling load of the vehicle. In view of privacy protection, a glass with relatively low visible light transmittance is preferably used for a rear window glass of a vehicle. Such kinds of glass include the followings.
For example, a dark gray colored infrared absorbent glass disclosed in Japanese Patent Publication No. 07-29813B consists of the soda-lime-silica glass including colorants consisting of 1.00 to 1.7 weight percent of Fe2O3 (total iron), at least 0.27 weight percent of FeO, 0.002 to 0.005 weight percent of Se, and 0.01 to 0.02 weight percent of CoO. The glass exhibits less than 32 percent of the luminous transmittance and less than 15 percent of the total solar infrared transmittance at 3.9 mm thickness.
A dark gray colored glass disclosed in Japanese Patent Publication No. 08-157232A consists of a soda-lime-silica glass including colorants consisting of 0.8 to 1.4 weight percent of Fe2O3 (total iron), less than 0.21 weight percent of FeO, 0.05 to 1.0 weight percent of TiO2, 0.02 to 0.05 weight percent of CoO, and 0.0005 to 0.015 weight percent of Se.
A neutral gray colored glass disclosed in claim 25 of U.S. Pat. No. 5,393,593 consists of a soda-lime-silica glass including colorants consisting of 1.00 to 2.2 weight percent of Fe2O3 (total iron), at least 0.20 weight percent of FeO, 0.0005 to 0.005 weight percent of Se, and 0.010 to 0.030 weight percent of CoO. The glass exhibits less than 35 percent of the luminous transmittance and less than 20 percent of the total solar infrared transmittance at 3.9 mm thickness.
A glass disclosed in PCT (Japanese phase) No. 07-508971 consists of a soda-lime-silica glass including colorants consisting of 1.3 to 2.0 weight percent of Fe2O3 (total iron), about 0.01 to 0.05 weight percent of NiO, about 0.02 to 0.04 weight percent of Co3O4, about 0.0002 to 0.003 weight percent of Se and 18 to 30 weight percent of a ferrous iron value, resulting in less than 0.53 of a light and shade coefficient.
In both the dark gray colored infrared absorbent glass disclosed in Japanese Patent Publication No. 07-29813B and the neutral gray colored glass disclosed in U.S. Pat. No. 5,393,593, a great quantity of Se is used for providing a desirable color. However, such a great quantity of Se is not favorable for the environment because Se is toxic and easy to vaporize. The above dark gray glass disclosed in Japanese Patent Publication No. 08-157232A including 0.05 to 1.0 weight percent of TiO2 as an essential component is not preferable because TiO2 is expensive to thereby increase a cost.
The aforementioned glass includes the high concentration of selenium to provide optical properties, essentially without including nickel.
The glass disclosed in PCT (Japanese phase) No. 07-508971 is prepared from a standard soda-lime-silica glass, to which iron oxide, cobalt oxide, nickel oxide and selenium are added in a specific ratio. However, the glass composition disclosed therein has the great concentration of selenium and a small amount of nickel oxide.
It is an object of the present invention to provide an ultraviolet/infrared absorbent low transmittance glass having a grayish green shade, a low visible light transmittance, a low solar energy transmittance and a low ultraviolet transmittance, thus it is useful for a window of a vehicle or a building, particularly for a privacy protecting glass of a rear window of a vehicle.
An ultraviolet/infrared absorbent low transmittance glass of the present invention is formed of a base glass and a colorant, wherein major constituents of the base glass are 65 to 80 wt. % of SiO2; 0 to 5 wt. % of Al2O3; 0 to 10 wt. % of MgO and 5 to 15 wt. % of CaO wherein a total amount of MgO and CaO is between 5 and 15 wt. %; 10 to 18 wt. % of Na2O and 0 to 5 wt. % K2O wherein a total amount of Na2O and K2O is between 10 and 20 wt. %; and 0 to 5 wt. % of B2O
Also, the colorant includes more than 0.95 and less than 1.2 wt. % of total iron oxide (T-Fe2O3) expressed as Fe2O3, i.e. 0.95 less than T-Fe2O3 less than 1.2; 0.001 to 0.03 wt. % of CoO; and 0.003 to 0.2% of NiO.
The glass of the present invention does not substantially contain Se. The glass of the present invention is preferable to be reinforced by blasting air cooling for a desired color shade.
Hereunder, embodiments of an ultraviolet/infrared absorbent low transmittance glass composition will be explained. It should be noted that components are represented in weight percentage.
SiO2 (silica) is a principal component of the ultraviolet/infrared absorbent low transmittance glass. Less than 65% of SiO2 lowers durability of a glass and more than 80% of SiO2 raises a melting temperature of a glass too high.
Al2O3 is a component for improving the durability of the glass. More than 5% Al2O3 raises a melting temperature of a glass too high. A preferable range of Al2O3 is between 0.1% and 2%.
MgO and CaO are used to improve the durability of a glass and adjust a devitrification temperature and a viscosity of a glass during molding. More than 10% of MgO raises the devitrification temperature. Less than 5% or more than 15% CaO raises the devitrification temperature of a glass. The durability of a glass is lowered when the total amount of MgO and CaO is less than 5%, while the devitrification temperature is increased when the total amount of MgO and CaO exceeds 15%.
Na2O and K2O prompt a glass to melt. An efficiency of promoting the melting becomes poor when Na2O is less than 10% or the total of Na2O and K2O is less than 10%, while the durability of a glass is lowered when Na2O exceeds 18% or the total of Na2O and K2O exceeds 20%. It is preferable for K2O not to exceed 5% because of a cost.
B2O3 is a component for improving the durability of a glass, prompting to melt, and yet enhancing the ultraviolet absorption. B2O3 should be less than 5%, since it becomes difficult to mold due to vaporization of B2O3.
Iron oxide is present in the form of Fe2O3 and FeO in the glass. Fe2O3 is a component for improving the ultraviolet absorption and FeO is a component for improving the heat rays absorption. The iron in the composition of the glass makes the glass green tint.
When a total amount of iron oxide (T-Fe2O3) expressed as Fe2O3 is less than 0.95%, the efficiency of ultraviolet and infrared absorption becomes too small to provide desired optical properties. On the other hand, when T-Fe2O3 exceeds 1.2%, it is difficult to obtain a desired grayish color shade because a large amount of iron makes the color green tint too much.
When T-Fe2O3 is not greater than 1.1%, iron in the composition is effective in coloring the glass green tint and improves the visible light transmittance, thus other colorants can be added to adjust the shade. T-Fe2O3 is therefore contained in an amount between 0.95% and 1.2%, preferably not more than 1.1%.
Fe2O3 particularly has a function of increasing the light absorption in the ultraviolet range when the glass is reinforced by air blast cooling. This means that the glass of this invention can obtain enough efficiency of the ultraviolet absorption without using expensive ultraviolet absorbent such as CeO2 and TiO2. When T-Fe2O3 is in the range mentioned above, the desired color shade of the glass can be obtained after discoloration due to the reinforcement process by the air blast cooling.
When the FeO/T-Fe2O3 ratio (a weight of FeO expressed as Fe2O3 against T-Fe2O3) is too low, sufficient heat ray absorption can not be achieved because the amount of FeO is too small. Also, many bubbles can be formed in a molten glass because the molten glass is relatively reactive with oxygen, so that a product yield is lowered. When the FeO/T-Fe2O3 ratio is too high, the visible light transmittance is reduced and the color becomes blue tint. In addition, nickel sulfide stones are sometimes present in the molten glass because the molten glass is relatively reductive. Too high ratio of FeO/T-Fe2O3 is also not preferable since it causes streaks with enough silica and silica scum.
In the present invention, the FeO/T-Fe2O3 ratio in a range between 0.15 and 0.4 brings a green shade, which is an almost neutral color having high ultraviolet absorption and high heat ray absorption. In this case, values expressed as Fe2O3 are used for the content of FeO.
CoO is a component for obtaining an almost neutral color such as greenish gray shade in cooperating with Se and/or NiO, and Fe2O3 for controlling the visible light transmittance. Less than 0.001% CoO can not form a desired color shade and makes the visible light transmittance too high. More than 0.03% CoO makes the color too blue tint and reduces the visible light transmittance. A content of CoO is preferable to be in a range of 0.001% to 0.018%.
NiO is a component for controlling the visible light transmittance and for reducing the excitation purity as like as CoO. It should be understood that NiO may not be always included when Se is included. When NiO is included more than 0.2%, nickel sulfide stones are sometimes present in a product and the visible light transmittance is reduced. In addition, the obtained shade becomes too greenish. When using NiO, the content thereof is preferably in a range between equal to or more than 0.003% and less than 0.05% for middle visible light transmittance, or in a range between 0.05% and 0.2% for low visible light transmittance.
When a concentration of NiO in the glass is too high, there is a possibility that NiO coagulates to form a nickel sulfide stone. However, when NiO is in the range defined by this invention, the desired color shade can be obtained without producing the nickel sulfide stone.
It is known that the coordination number of NiO varies according to a rate of cooling a glass so that the color of the glass varies. This is because the cooling rate changes the coordination number of oxide around Ni2+ from 6 to 4 and thus changes the optical absorption. The absorption of Ni2+ with octahedral coordination exists around 430 nanometer to thereby impart yellow to the glass, while the absorption of Ni2+ with tetrahedral coordination exists between 500 and 640 nanometers. Therefore, the excitation purity would be reduced to obtain the preferable shade when using Ni2+ with tetrahedral coordination. A windshield of a passenger car is normally reinforced by air blast cooling for safety. The reinforcement process by air blast cooling also changes the coloring condition of NiO. In the present invention, the desired color shade can be obtained through the discoloration from the reinforcement process by the air blast cooling without adding Se.
CeO2 is a component for improving the ultraviolet absorption and is present in the form of Ce3+ or Ce4+ in the glass. Particularly, Ce3+ is effective in absorbing ultraviolet light with less absorption of the visible light. In the present invention, an oxide of Ce3+ is also expressed in terms of CeO2 and is included in the total amount of CeO2.
TiO2 is a component for improving the ultraviolet absorption particularly by interaction with FeO. TiO2 can be added to improve the ultraviolet absorption within such a range as not to lose the grayish green color shade, or to add a yellow tint in order to obtain the desired color shade. The use of expensive CeO2 and TiO2 increases the cost so that it is not preferable to use more than 2% CeO2 and TiO2.
One or more than two ingredients among MnO, V2O5, MoO3, CuO, and the like may be added as colorant, and SnO2 within a rang from 0% to 1% in total amount may be added as a reducing agent in such a range as not to lose middle transmittance and the grayish green shade. There is substantially no Cr2O3 contained except a trace amount from raw materials as an impurity, which is very difficult to eliminate. To further securely prevent the formation of nickel sulfide stones, ZnO may be added in a range from 0% to 1%.
In the present invention, the glass is preferable to be reinforced by the air blasting. The desired color shade and optical properties are obtained in the reinforced process when the glass has a composition of the present invention comprising NiO and Fe2O3 in the specific amount.
In the reinforcement process, the glass plate produced from the molten glass is reheated at 600 to 750xc2x0 C. for 2 to 5 minutes, and then, cooled by blasting air of 10 to 30xc2x0 C. at a cooling rate of 100 to 300xc2x0 C./sec.
The air blasting reinforcement process makes the glass plate comprising NiO and Fe2O3 have the greenish gray and almost neutral shade, and have the low visible light transmittance and the low ultraviolet transmittance while keeping an ability of absorbing the high heat rays.
In the present invention, when measured by using C.I.E standard illuminant xe2x80x9cAxe2x80x9d, the glass with a thickness between 2 to 5 mm has a visible light transmittance (YA) in a range from 10% to 50%, a solar energy transmittance (TG) of not greater than 30% and an ultraviolet transmittance (Tuv) defined by ISO of not greater than 12%.
When using the color system of L*, a*, b*, the chromaticity, expressed as a* and b* of the glass color, is preferably in a range of xe2x88x928xe2x89xa6a*xe2x89xa6xe2x88x922 and xe2x88x922xe2x89xa6b*xe2x89xa64, respectively.
When measured by using C.I.E. standard illuminant xe2x80x9cCxe2x80x9d over the wavelength range between 380 and 770 nanometers, the glass of the present invention preferably has optical properties with a dominant wavelength (xcexd) in a range between 480 and 580 nanometers and an excitation purity (Pe) of less than 9% in a case the glass has a thickness of 4 mm.
Hereinafter, a mode of carrying out the present invention will be described with reference to examples.